THE CESTOIDEA 



105 



,,The neck bears the head or "scolex," which is usually regarded 

 as^the anterior end of the worm, but which is more probably the 

 morphological posterior end. It is here flattened in a plane at 

 right angles to that of the proglottids, viz. from side to side ; its 

 dorso-ventral diameter being greatest; the dorsal and ventral 

 surfaces are therefore narrow, along each there is a narrow but 

 deep sucking groove or " bothrium," elongated in the direction of 

 the scolex (Fig. III. 2). The wall of the bothrium consists of 

 bundles of muscles which are not limited internally from the paren- 

 chymal tissue (Fig. IV.). 



In respect of the general microscopic structure, it is unnecessary 

 to confine ourselves to a type. The body of the Cestoidea is 

 covered by a cuticle (non-chitinous, according to Leuckart, and 



FIG. IV. 



B. microcephfilus, Rud. A trans- 

 verse section of the scolex. ( x 50, 

 orig.). D and V indicate the 

 dorsal and ventral sucking grooves 

 or bothria. The substance of the 

 scolex consists chiefly of muscle 

 fibres arranged in three main 

 lines, viz. dorso- ventral, trans- 

 verse, and oblique, the direction 

 of each of which is modified by 

 the outgrowth (a) to form the 

 sides of the sucking grooves ; b, 

 the main excretory canal, branches 

 of which are also shown in various 

 parts of the scolex ; c, the edge 

 of the ganglion and the uppermost 

 part of the main lateral nerve, 

 with accessory nerves passing 

 away. 



containing CaCo 3 ) which is of variable thickness. Probably in the 

 primitive Cestodes the cuticle bore small spinelets over the whole 

 surface of the body, as in Gyrocotyle; but in the majority these have 

 disappeared from the general surface of the body, and remain only 

 in the cirrus (or penis) of many genera, while in various parts of 

 the organs of fixation they have become greatly enlarged to form 

 booklets. 



The cuticle consists of two to four layers (see Zernecke (51), 

 etc.), the outermost of which generally appears as if composed of 

 short, close-set " hairs," corresponding with the outermost layer of 

 Trematodes, and this appears to be shed periodically (Fig. V.). 

 The deepest layer is always distinguishable as a thin membrane 

 differing from the rest ; this is the basement membrane, produced 

 by the parenchymal cells (Blochmann, Trematode literature, 8) ; the 

 rest of the cuticle is produced by the " subcuticula," and is traversed 

 by fine canals (in Ligula, Taenia, and others) which contain either 



